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How do I add more horsepower to a 1994 Mariner 115hp

O

overboardmarine

Member
"I have a very healthy 1994 Ma

"I have a very healthy 1994 Mariner oil injected 115hp. I am looking to put it on a 1985 20' Advantage low profile hull. It is a nice sturdy boat which typically calls for 150-235hp. I'm okay with less speed from installing the 115 but are there any simple bolt HP on tricks that don't compromise reliability? I know sometimes changing jets in the carbs sneaks a little added HP out. Are there any websites out there that will calculate the hull's likely top speed with the 115hp?. Please advise, thanks."
 
"If you want to up the horsepo

"If you want to up the horsepower - sell your nice 115 and buy a similar vintage 200.

I can calculate approximate maximum top speed (and will post after completed).

Any motor should match the rig. In most cases you want to hang 80% of the max rated horsepower off the back of the boat.

If the max rating is in fact 235 - then 235 x .8 = 188 horsepower (175 or 200) is your choices.

Your 94 model was not the Merc 2L head, it was a 1.8 (plus a little). It's max horsepower capability without major machine work is 125 horses - not worth the cost of the parts to gain only 10 more horses - you can't simply re-jet, you need new carbs.

You are definately going to have to re-prop the motor to a lower pitch. You could take that opportunity to go to a "high flow" hub such as Solas or any of the Flo-Torque hubs - that can get you 5-10% better results compared to a standard OEM props.

Other than that, keep the hull very clean, change the spark plugs annually, and always run fresh gas (none more than 2 weeks old).

If there was an easy or magic solution to make a 115 run like a 175, they wouldn't build the 175
"
 
"Here's the rough numbers

"Here's the rough numbers for your rig with different horsepowers on board. All calculations assume a prop matched to the particular motor and hull - at sea level, calm water, no wind, temp 77 degrees, humidity 30% and barometric pressue 29.6...

If that sounds like alot non-sense, that is exactly how all the mfg's rate horsepower. If any of those factors are different you lose horsepower. Temp and humidity are the worst factors. Temps in excess of 80 degrees with high humidity can rob your motor of as much as 15 percent of it's horsepower. Therefore in the summer you should run a prop with less pitch than you do in the spring/fall (and winter if you have a suitable climate to run).

Anyhow, read horsepower - top speed (all motors rated were Merc/Mariner 2 stroke Carburated Models - non DFI (not OPTI's))

115 32
135 34
150 36
175 39
200 42"
 
Thanks Graham. Looks like I ne

Thanks Graham. Looks like I need to settle for the slow lane with the 115hp or trade it for some more horses. Appreciate your help.
 
"I guess it really depends wha

"I guess it really depends what your expectations are and the purpose for the boat.

If you are looking to tear up and down the lake or tow a wake board/skier tube whatever, you are probably underpowered, but if you are just doing general cruising, run canals etc, the 115 will use a whole lot less gas and push her along somewhere in the mid-20's really nice...

If you are going to make a switch, I would look for a nice used (mid/late 90's) EFI. It would minimize the fuel consumption difference in going to a larger horsepower - and your 115 is actually a popular motor (especially in the 17' aluminum range). You could probably break even on the upgrade, depending where you live..."
 
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